Method and device for monitoring and maintaining correct regulation of the tension of a yarn fed to a textile machine

Abstract: A method for monitoring and maintaining correct regulation of the tension of a yarn (1) fed to a textile machine (T), such as a loom, a hosiery machine or a knitting machine, comprises continuously determining both the state of movement and the tension of the yarn (1) at a point between the usual bobbin (2) from which the yarn is unwound and the textile machine (T) which processes it, then comparing the measured tension with a preset desired tension and adjusting said tension of the yarn (1) at a point between the bobbin (2) and the point in which the said tension is measured, said adjustment being interrupted when the measured tension is equal to the desired value. A device for implementing the aforesaid method comprises tension sensing means connected to means for comparing the measured value with a desired tension, said comparison means cooperating with means for controlling braking means acting on the yarn so as to vary its tension in the desired manner.

Description: This invention relates to a method for monitoring the tension of a yarn fed to a textile machine and for regulating it in such a manner as to maintain it constant, ie equal to a predetermined tension, said yarn being unwound from a usual support such as a bobbin or the like and being fed to said machine, such as a usual loom, a hosiery machine or a knitting machine. The invention also relates to a device for implementing said method. Methods and devices are already known for varying the tension of yarn fed to a textile machine in accordance with particular processing stages of the machine or particular requirements of the user. A known tensioning device (such as the device disclosed, for example, by DE-A-3 734 471) comprises for example two opposing disc elements which are pressed together and against an interposed yarn by a helical spring; the action of this latter on the discs is adjusted by a knob which is screwed onto a threaded rod to vary the pressure exerted by the discs on the yarn. In this manner the yarn is braked and its tension varied. Another known device (such as the device disclosed, for example, by DE-A-3 734 471) comprises a series of fixed pins arranged in such a manner as to compel the yarn to travel over them and undergo a zig-zag path enabling the yarn to be braked or tensioned; by varying the relative spatial position of said pins the path angles can be varied discretely, so adjusting the tension applied to said yarn. These devices and their adjustment methods, together with other known devices and methods, enable the yarn to undergo the required tensioning or braking. This tension varies during the use of the yarn even if it originates from a single support member or bobbin. In this respect, the yarn of each bobbin has a starting tension or braking which varies depending on the yarn colour, its type, its lubrication and the relative humidity of the environment in which the yarn is processed, but in particular on the bobbin diameter. The yarn bobbin diameter is known to gradually decrease as the yarn is unwound from the bobbin. Hence the rotational speed under which the yarn is unwound increases in a manner inversely proportional to the bobbin diameter, this increasing the yarn tension. In addition, if the speed of the textile machine increases there is a proportional increase in the tension applied to the yarn. The aforesaid known devices are unable to independently compensate for the continuous variation in the tension of the yarn during its use in the production of an article. All this results in various processing problems in textile machines, which affect product quality in addition to resulting in a wastage of yarn used in producing the article. In particular, in knitting and hosiery machines, because of the non-uniformity of the yarn tension, articles are produced without a constant length or width. This makes it difficult to maintain a given size to be produced. In addition, in the case of hosiery this makes it necessary to carry out a final control of the product (matching) consisting of grouping together stockings of a fairly similar length to form pairs. This results in evident high production costs to be added to the excessive use of yarn. In this respect an article longer or wider than required obviously uses a wasted quantity of additional yarn. The aforesaid known devices and methods are unable to independently and automatically compensate for the said tension variation. Consequently, in an attempt to maintain yarn tension variations within acceptable limits, operators or users of textile machines are compelled to continuously control the yarn fed to these machines in the sense of continuously measuring its tension and acting on braking device to control them in such a manner as to return the tension to within a range of acceptable values. DE-A-3734471 discloses a method for determining the tension of a yarn unwound from a bobbin and fed to a rotating package or winding bobbin of a winder or winding machine. The measured tension is then compared with a preset desired tension value, the yarn tension being adjusted at a point between the bobbin and that in which the said tension is measured. The adjustment is interrupted when the measured tension is equal to the desired value. The prior art also discloses a device for implementing the above method in which a piezoelectric element is used as means for sensing the tension of the yarn, said piezoelectric element generating discrete output signals corresponding to the measured yarn tension and the yarn movement. Said element is connected to means for comparing the measured tension with a preset desired tension, said comparison means cooperating with means for controlling braking means acting on the yarn; the control means act on the latter on the basis of the comparison effected by the comparison means in order to make the yarn tension equal to the desired value. An object of the present invention is to provide a method and relative device for monitoring and maintaining correct regulation of the tension to which the yarn is subjected during its feed to a textile machine, and in particular for maintaining this tension substantially constant or at least close to a desired value. A further object is to provide a method and relative device for halting the textile machine when, because of a defect in the yarn bobbin or because of hindrance to the free running of the yarn, this assumes and unwinding tension even slightly greater than the desired value. A further object of the invention is to provide a device which enables the tension of the yarn fed to the textile machine to be constantly displayed, so providing the user or operator with immediate information regarding the tension of the yarn of each yarn fed to the machine. A further object is to provide a device able to sense whether the yarn is running or not running on the basis of the instantaneous variations in the yarn tension, said device halting the machine and activating a machine alarm signal if the yarn under control is broken or missing. A further object is to provide a device which enables the yarn tension to be easily varied on the basis of processing needs, for example to achieve in sock or knitwork production a narrowing of the stitch at desired points such as the ankle or rib of socks, so enabling the shape of the article to be modelled at will. A further object of the invention is to provide a device for monitoring and maintaining a correct and desired yarn tension or braking which is free from maintenance or cleaning problems. A further object of the invention is to provide a device of simple and economical construction, which is of extremely compact size and can be easily used in any type of textile machine. These and further objects which will be more apparent to the expert of the art are attained by a method as described in the characterising part of the corresponding independent claim. The above objects are also attained by a device in accordance with the characterising part of the corresponding independent claim. The present invention will be more apparent from the accompanying drawing, which is provided by way of non-limiting example and in which: Figure 1 is a block scheme of the device according to the invention; Figure 2 is a side view of an embodiment of the device of Figure 1; Figure 3 is a front view of the device of Figure 1; Figure 4 is a different embodiment of part of the device of Figure 1; Figure 5 shows the main flow diagram of the operations performed by the device implementing the method of the present invention; and Figure 6 shows the flow diagram of the interrupt routine of the main flow diagram shown in Figure 5, said routine being effected at predetermined constant intervals. With reference to Figures 1 to 4, the device according to the invention operates on a yarn 1 fed from a bobbin 2 in any known manner to a textile machine T, such as a loom or a hosiery or knitting machine. According to the invention, the yarn 1 cooperates with a tension sensor, preferably a known extensometer able to provide an electrical signal proportional to the tension of the yarn with which it cooperates. This sensor can also be a usual piezoresistor or the like (which, as in the case of the extensometer, can be used to form static load cells as utilized in usual weighing devices) or known pressure sensors. The sensor 5 (positioned between the bobbin 2 and the machine T) is connected to a comparison and control unit 6 via an amplifier 7 for the signal emitted by the sensor 5 and an analog/digital converter 8 which arranges said signal for acceptance by the unit 6. This latter is preferably a microprocessor. However it can also be in the form of usual electrical and/or electronic components defining a circuit able to detect and treat analog signals, in which case the converter 8 is not used. The comparison and control unit is connected to a display 10 for displaying the tension of the yarn under control, and to an interface 11 (such as a usual keyboard) enabling reference data to be fed to the unit. These data are preferably: a) data concerning a desired yarn tension value; b) data concerning the acceptable tolerance on the desired value; c) data concerning an acceptable instantaneous peak tension value. By means of the display 10, the unit 6 continuously displays the tension of the yarn 1 during its feed to the machine T and provides the user or operator with real time information of the yarn tension. Obviously, if the machine T operates on more than one yarn (such as a stocking production machine) each sensor 5 is connected to the unit 6 which by means of the display informs the user of the tension of each yarn; this can be achieved for example by providing a display which displays the tension of all yarns simultaneously, or by providing a display which shows the tension of all yarns in a cyclic and sequential manner. The control unit 6 is connected to a braking member 15 operating on a corresponding yarn directed towards the machine T, said member 15 being able to vary the yarn tension (or braking). By means of the member 15 (positioned between the bobbin 2 and sensor 5) the unit 6 is therefore able to vary the tension in the yarn 1 whenever the information obtained by the corresponding sensor 5 deviates from the desired value to the extent of falling outside the acceptable tolerance range. In one embodiment of the device of the invention shown in Figures 2 and 3, the braking member 15 is fork-shaped and comprises a support 16 from which there perpendicularly extend two parallel arms 17. These are formed of an antifriction material (ceramic, alumina or the like) and cooperate directly with the yarn in such a manner that it forms angles α and β to the direction from which it arrives from the bobbin 2 or to the direction in which it is fed to the machine T which are varied in accordance with the desired tension for the yarn processed by said machine. For this purpose (ie to vary the said angles) the support 16 is associated with the output shaft 20 of an electrical and/or hydraulic and/or pneumatic and/or magnetic actuator, for example an electric motor 21 preferably of stepping type, the operation of which is controlled by the unit 6. Alternatively, the member 15 could be one of a plurality of different constructions, one of which comprises two opposing discs 23A and 23B cooperating with the yarn with their frusto-conical portion 22, said discs being mounted on a shaft 24 on which there is also mounted a compression spring 26. The disc 23A rests against a shoulder 28 whereas the disc 23B cooperates directly with the spring 26 and is urged thereby against the disc 23A so as to clamp with this latter the yarn 1 present between them and brake its movement (hence varying its tension). The spring 26A is subjected to the action of a pusher element 29 slidable along the shaft 24 by a known hydraulic and/or pneumatic piston 30 fed and moved by a usual actuator member 31, the operation of which is controlled by the unit 6. By varying the thrust of the disc 23B against the disc 23A the tension in the yarn 1 can be varied by virtue of the variation in its braking. As can be seen in Figures 2 and 3, the device of the invention comprises a one-piece body 33 containing the aforestated elements defining the invention. The body 33 comprises arms 34, 35 and 36 provided with yarn guide holes 37 through which the yarn 1 slides. The body 33 can also be provided with a plurality of holes 37 and/or members 15 to be able to cooperate with a plurality of yarns fed to a knitting or hosiery machine. Alternatively a plurality of bodies 33 (without the unit 6, the interface 11 or the display 10) cooperate with respective yarns 1 and with a single control unit 6 connected to said interface and to the display. Finally, the unit 6 cooperates with the textile machine to halt its operation whenever the sensor 5 senses a yarn tension greater or less than the desired value and laying outside the acceptable tolerance range (caused for example by a defect in the bobbin 2 or a hindrance of any kind to the free movement of the yarn), or a tension peak (caused for example by the yarn being locked on the bobbin). This prevents breakage of the yarn 1 and enables a substantially uniform quality to be maintained for the article produced by the machine 1. The method of the invention will now be described in relation to the use of the aforesaid device. It will be assumed that a yarn 1 is fed to the machine T. To facilitate the initial movement of the yarn, the braking member 15 does not initially act on it (for example the discs 23A, 23B are spaced apart). By means of the sensor 5 the unit 6 detects whether the yarn is moving, for example by sensing a continuous tension variation (moment by moment). Using suitable algorithms this enables the unit 6 to sense whether the yarn is moving. If however the unit does not sense instantaneous variations in the yarn tension it considers that the yarn is not moving and activates usual devices for halting the textile machine and/or warning devices (acoustic and/or light-emitting), not shown, to indicate the stoppage of the yarn and/or its absence and breakage or its undue movement. The device of the invention is therefore also able to detect whether the yarn fed to a textile machine is moving or not, and to advise the user of any abnormalities in the feed to said machine. Alternatively, a usual known movement sensor connected to the unit 6 can enable this latter to determine whether said yarn is moving or not. Having sensed that the yarn is moving, the unit 6 switches to the tension control stage. If this tension is different from the desired value, the member 15 is activated to vary its braking action on the yarn and return its tension to the desired value (preferably the average value of a range of predetermined measurements). The action of the member 15 terminates when the tension reaches the desired value. If this again varies, the member 15 again operates under the control of the unit 6 as previously described. In this manner said tension is constant for the entire duration of production by the machine T, the articles then possessing a reliable uniformity of quality. The operation of the unit 6 (continuous during yarn feed to the machine T) will now be described in detail with reference to Figures 5 and 6. In these latter the blocks defining the operational stage of the unit 6 are marked by a reference numeral, by which they will be indicated. With reference to Figure 5, in a first stage 50 the unit 6 is reset and then initialized in stage 51, so arranging it for operation. The number of measurements (CNT) to be made for calculating an average tension with which to compare the instantaneous values measured during the use of the yarn is then defined (for example twenty measurements), together with the maximum number of attempted but unsuccessful adjustments (CNT ALT) when an instantaneous tension different from the desired tension is measured (for example 30 adjustments). This is represented by block or stage 52. The time interrupt routine (INTERRUPT) (block or stage 53) is then activated, resulting in the performance of the interrupt routine steps shown in Figure 6, which are performed at predetermined constant intervals. In stage or block 54 the unit 6 is fed with and memorizes (via the interface 11) the desired theoretical tension data (TENS-T), the tension tolerance (TENS-ER) and the peak tension (PEAK-T); in stage or block 55 the display is set to show, if there is no alarm, whether the yarn is at rest or moving and also the measured tension (TENS-M), or, in the case of alarm, whether there is yarn breakage, tension out of tolerance or peak tension. During performance of the interrupt routine (Figure 6), the unit 6 receives in stage 56 the tension signals (TENS) from the sensor 5 and compares them with the memorized peak value (PEAK-T, stage 57). If the tension is greater than the peak tension, the unit 6 activates an alarm (block 58) and halts the machine. The unit 6 displays the stoppage (stage or block 55) on the display 10. If the tension is not greater than the peak tension, the unit 6 calculates the average tension of the counts made (block 61), after decrementing the counter CNT (relative to the number of measurements made, block 60) to zero and then reloading it in block or stage 62 (as indicated in the relative blocks). The calculation of the average is made only if in stage 60 the value of the counter CNT decremented by one at each measurement is equal to zero. Then following the steps of blocks 61 and 62 or of block 60 alone, the difference between the current tension and the previous tension is calculated (block 63). If these are equal, the yarn is considered at rest (block 64) and the unit 6 indicates "yarn stoppage" to the machine and displays it (block 55). If they are not equal, the unit 6 senses that the yarn is moving (block 66) and commences the actual tension adjustment stage (blocks 67-71-72). During this stage, the unit 6 checks (blocks 67 and 68) whether the measured tension is within tolerance; if it is not, the unit 6 acts on the braking member 15 which brakes the yarn 1 to increase its tension (block 71) or slackens its action on said yarn (block 72). If the tension is within tolerance, the unit 6 senses this (block 69) and reloads the counter relative to the number of adjustments attempted without success CNT ALT (block 70). If adjustments have been made (blocks 71, 72) the counter CNT ALT is decremented by one (block 73) and if its value reaches zero after a number of consecutive adjustments the program returns to block 58 and the machine T is halted. If not, the unit terminates the interrupt routine and again operates in accordance with the flow diagram of Figure 5 from the point at which it was interrupted. It then checks if any alarm device has been activated (block 4 of Figure 5) and whether a usual reset button has been pressed (block 75 of Figure 5); if the reply is positive, the unit 6 cancels any machine stoppage and activated alarm indication and repeats the aforesaid measurement, adjustment and control cycle stages. Consequently if the desired tension cannot be maintained, the unit 6 halts the machine. If it can be maintained, then the machine continues to operate without interruption and the measured tensions are shown on the display 10. In addition to the connections described in relation to Figure 1, the unit 6 comprises connection points 90 and 91 for communication with a usual known unit (not shown) for controlling the production functions of the machine T. Digital signals can be fed via these points to the unit 6 to increase and decrease at will and/or automatically, depending on processing requirements, the desired tension preset in the unit 6 via the interface 11. The unit 6 comprises a further connection point 92 for feeding analog signals (for example via a potentiometer) corresponding to the said digital signals, to the unit 6. The parameters memorized in the unit 6 can be modified via the points 90, 91 or 92 in accordance with processing requirements, for example to obtain when producing socks or knitwork a narrowing of the product at desired points (such as the ankles and rib of socks), so enabling the shape of the article produced to be modelled at will. In the case of yarn-working textile machines operating on more than one yarn, the tension of the various yarns can be regulated simultaneously via the points 90, 91 and 92 (for example with the unit connected to the points 90 and 91), so avoiding having to adjust the tension of each yarn. The device of the invention enables yarn tension (or braking) to be regulated without having to be maintained or cleaned, in that as said device adjusts the yarn tension on the basis of a measured value, it can never be influenced by any dirt accumulation in the braking member 15 (which in the case of normal disc-type yarn brakes causes them to open and hence no longer able to effect controlled braking). One embodiment of the device of the invention and the method implemented by it have been described. Other embodiments are however possible in the light of the aforegoing description and are therefore to be considered as falling within the scope of the present document.

Claims: A method for monitoring the tension of a yarn fed to a textile machine and for regulating it in such a manner as to maintain it constant, ie equal to a predetermined tension, said yarn being unwound from a usual support such as a bobbin or the like and being fed to said machine, such as a usual loom, a hosiery machine or a knitting machine, comprising the step of continuously determining, at a point between the usual bobbin (2) from which the yarn is unwound and the textile machine (T), whether the yarn is moving between the bobbin (2) and the textile machine (T), in which case the tension of said yarn (1) is measured and the measured tension then compared with a preset desired tension value, said tension of the yarn (1) being adjusted at a point between the bobbin (2) and that in which the said tension is measured, said adjustment being interrupted when the measured tension is equal to the desired value. A method as claimed in claim 1, characterised in that the determination of whether the yarn is moving is effected by ascertaining the variation in the measured tension. A method as claimed in claim 1, characterised in that the comparison between the tensions is made between an average value of measured tensions and a preset tension. A method as claimed in claim 1, characterised in that the comparison between the tensions is made between the measured tension and a preset peak tension. A method as claimed in claim 1, characterised by indicating, and/or halting the textile machine (T), when at least one irregularity between the measured tension and the desired or preset tension is noted. A method as claimed in claim 1, characterised by halting the textile machine (T) if a discrepancy is determined between the measured tension and the desired tension for a predetermined consecutive number of times, or if a predetermined number of successive adjustments of the tension of the yarn (1) fed to the machine (T) are made without this tension equalling the desired tension. A method as claimed in claim 1, characterised by displaying the measured and preset tensions. A device for implementing the method claimed in claim 1, comprising means for continuously sensing and determining the movement of at least one yarn (1) and means (5) for sensing the tension in this latter, both said sensing means being connected to means for comparing the measured tension with a preset desired tension, said comparison means cooperating with means (6) for controlling braking means (15) acting on the yarn (1), said control means (6) acting on these latter on the basis of the comparison effected by the comparison means in order to make the yarn tension equal to the desired value. A device as claimed in claim 8, characterised in that the tension sensing means (5) and the movement sensing means are positioned between the bobbin (2) and the textile machine (T), and consist of a single sensing means. A device as claimed in claim 8 or 9, characterised in that the movement and/or tension sensing means (5) are at least one extensometer. A device as claimed in claim 8 or 9, characterised in that the movement and/or tension sensing means (5) are at least one piezoresistor. A device as claimed in claim 8, characterised in that the comparison means and control means are a single control unit (6), preferably a microprocessor. A device as claimed in claim 12, characterised in that the control unit (6) is connected to the textile machine (T) and controls its stoppage on the basis of the comparison between the measured tension and the preset tension, said unit (6) being also connected to acoustic and/or visual indication means. A device as claimed in claim 12, characterised in that the control unit (6) is connected to a plurality of tension sensing means (5) and braking means (15) cooperating with corresponding yarns fed to the textile machine. A device as claimed in claim 12, characterised in that the control unit (6) cooperates with at least one usual unit for controlling the operation and production of the textile machine (T). A device as claimed in claim 8, characterised in that the braking means are a fork-shaped element (15) comprising arms (17) associated with a support element (16) which is connected to the output shaft (20) of an electrical and/or hydraulic and/or pneumatic and/or magnetic actuator, such as an electric motor (21), preferably of stepping type, controlled by the control means (6). A device as claimed in claim 8, characterised in that the control means(6) cooperates with a display (10) for displaying the measured instantaneous tension and with an interface (11) such as a keyboard or the like. A device as claimed in claim 8, characterised in that at least the tension sensing means (5) and the braking means (15) are associated with a single one-piece body (33) comprising a yarn guide (37) for directing the yarn (1) towards said means (5, 15).

Inventors: BAREA TIZIANO, BAREA, TIZIANO
Applicants: B T S R INTERNAT S P A, B.T.S.R. INTERNATIONAL S.P.A.
Application year: 1994
Main classification: B65H59
IPC codes: B65H59, D04B35, D03D49